One of the most common packaging materials in present use is a combination of various layers of paper to form the corrugated paper product generally referred to as corrugated cardboard or simply cardboard. In general, this rather familiar material typically consists of at least two layers of generally flat paper between which is sandwiched a layer of corrugated or "fluted" paper. The resulting composite laminated structure is generally far more rigid than the paper materials from which it is formed, and is an excellent packaging material for many applications.
Such corrugated cardboard is typically formed in a sequence of relatively well known operations. First, a paper web is typically drawn from a supply roll and is drawn into a device known as a "single facer." A second paper web is drawn from a second supply roll and is also fed into the single facer. The single facer subjects one of the webs to heat and moisture, usually in the form of steam, and then advances it between a pair of ribbed rollers which distort the paper into its fluted or rippled configuration. Glue is then applied to the fluted web, usually on the tips of the flutes on one side of the web, and then the second web is brought into contact with the glue-carrying side of the fluted web. When the two webs are so fastened together, the resulting composite is generally referred to as a "single face web." The single face web is then advanced to another station generally referred to as a "double backer," as is yet another paper web generally referred to as a "liner." In the double backer, glue is typically applied to the corrugated portions of the single face web opposite the first liner and the second liner is then applied to the single face web to result in the cardboard construction in which the two flat layers of paper have the fluted layer sandwiched between them.
In typical operations, the various supplies of paper are kept on large rolls on the floor of a factory. Other portions of the machinery are kept directly above the supply rolls on a structure which is generally referred to as a "bridge conveyor" or just a "bridge." Typically, once the single face web is put together, it is forwarded along the bridge or bridge conveyor while the second liner which will complete the cardboard structure is advanced below the bridge or bridge conveyor.
In particular situations, the bridge conveyor can be used to temporarily store relatively large quantities of single face web to thereby form a buffer or an accumulator for the double backer if the single facer is slowed down or stopped for any reason. Alternatively, if the double backer is slowed or stopped, the bridge conveyor allows the single facer to run at normal speed and build up a supply of single face web on the bridge conveyor. In particular applications, the extra time that the single face web spends on the bridge conveyor prior to reaching the double backer gives the glue extra time for drying and bonding, resulting in better overall resulting structure.
Although the accumulator is useful for these purposes, the single face web that is allowed to loosely accumulate must generally be re-tensioned prior to entering the double backer. Accordingly, a corrugator line will also include some type of tensioning device for this purposes. Typical corrugating lines also include equipment which preconditions the various webs, using either heat or moisture or both prior to their reaching either the single facer or the double backer or both.
One constant problem with such corrugating lines or systems is the misalignment of the single face web and the liner when they are brought together at the double backer. As stated earlier, the single faced web is typically carried on a bridge conveyor while the liner is carried below the bridge conveyor. Although the various equipment for advancing the single face web and the liner can be aligned to a certain degree, there are always variations between the two. As a result, when the single face web and the liner are brought together in the double backer, the resulting cardboard will typically have edge portions which are uneven; i.e. the respective edge portions of the single face web and the liner will not match. In order to cure the misalignment, the cardboard typically has to be formed larger than its desired size and its edges trimmed of the respective excess.
For example, in the cardboard industry about 0.4 percent of production typically ends up as waste material directly attributable to the misalignment of the single face web with the liner. Because paper plants may average on the order of 50,000,000 square feet of product per month, even such a relatively small percentage would result in 200,000 or more square feet of alignment related scrap. Based on the cost of paper, the resulting loss can be tens to hundreds of thousands of dollars per year. Accordingly, various systems have been developed for attempting to accurately and precisely align a single face web with a liner. In some fashion, all of these systems incorporate either manual or automated sensing of the position of the single face web with respect to the liner, combined with some system for moving either the single face web or the liner to bring them into alignment with one another.
In one type of system, the alignment of the single face web and the liner is observed following their exit from the double backer and adjustments are made upstream along the corrugator line to correct the misalignment. This eventually improves the alignment, but a great deal of misalignment and resulting waste continues even following adjustment because of the relatively long distances in certain corrugating lines between the point at which the web or liner can be aligned and the point at which they are joined in the double backer and then observed as to their alignment.
In other types of systems, various mechanical devices are used to align the web and the liner such as edge guides and roller systems. Edge guides are disadvantageous because they move the web or the liner by pushing laterally against the edge of the web or liner, a technique which almost inevitably damages the edge being pushed so that the corrugated board which emerges from the double backer is still defective along one or the other or both of its edges, thus nullifying any advantages of the alignment.
Other aligning devices comprise the so called paper steering assemblies which require that various rollers underneath the moving web or liner be raised or lowered or otherwise maneuvered in a fashion which tilts the web or the liner to thereby encourage it to move to a different position. Needless to say, such devices, although conventional can be rather complicated and difficult to adjust precisely because of the secondary manner in which they align the web and the liner.
Yet other techniques attempt to align the web and the liner at a point well upstream of the point where tension is typically applied to both prior to their being forwarded into the double backer. Although this theoretically has the advantage of aligning the single face web and the liner when they are not under tension and therefore less likely to be damaged, in reality the far upstream alignment of the two provides continued opportunity for them to become misaligned again before they enter the double backer.
Additionally, those familiar with the manufacture of corrugated products also recognize that waste can occur in the original manufacture of the single faced web at the single facer and also during the slitting-scoring process that usually takes place following the manufacture of the double backed web.
In a typical single facer, two paper rolls each feed respective supplies of paper into the single facer. One is formed into the fluting, the other is joined to the fluting as the liner to form the single face web. Where the two paper supply rolls or the paths of paper that lead from them are misaligned, the resulting single face web will be characterized by excess fluting on one edge and excess liner on the other, both of which will eventually need to be trimmed, adding to the waste problem described earlier.
At the other end of the corrugating line, the slitter-scorer is the device that both cuts the corrugated product into various shapes that can later be made into packages, and also scores the corrugated board so that it will fold along certain lines as it is being manufactured into a typically rectangular package. A typical finished corrugated board will generally move laterally with respect to its path of travel depending upon the movement of the corrugator belt in the double backer. As a result, the position of the corrugated board is not fixed when it leaves the double backer and in order to produce an accurate package precursor, the slitter-scorer must be aligned with the corrugated board.
Accordingly, it is an object of the present invention to provide an apparatus and method for aligning a single face web and a liner, or several webs with each other and with a liner, in which the respective positions of the single face web and the liner are determined with a high degree of accuracy and precision and in which the position of the single face web or liner can be continuously accurately and precisely adjusted, especially in small known and desired increments, to bring the single face web and the liner into alignment. Furthermore, the determination of the alignment or misalignment of the web and the liner should take place relatively close to the position at which the two paths are adjusted so that the potential for the web and liner to become misaligned between the point of adjustment and the point of observation is substantially or totally eliminated.
It is a further object of the present invention to provide a method of producing slit or slit and scored pieces of finished corrugated board from a paper web material while minimizing or substantially eliminating waste during the production of the single face web, during production of the corrugated board, and during the slitting and scoring of the corrugated board into a package precursor.